1. Field of the Invention
This invention relates to circuit switchgears (service plugs) that can open electric circuits to interrupt circuit current. More specifically, the invention is directed to a service plug for use in closing and opening high-voltage circuits and large-current circuits that include wiring harnesses in electric cars and the like.
2. Background
For example, a conventional switchboard for a high-voltage circuit has been designed in the following manner. When a cover of the switchboard is opened, a male connector fixed to the cover is pulled out of a corresponding female connector fixed to a main body of the switchboard, thereby electrically interrupting the conduction of the high-voltage circuit. Therefore, considerations are given so that there is no possibility that the operator erroneously touches the electrodes and receives an electric shock.
On the other hand, a transportation equipment such as an electric car includes a high-voltage section for driving a motor. Therefore, considerations must be given so that there is no possibility that the operator receives an electric shock when he or she services a vehicle. Particularly, since specialists and also ordinary people can be involved in car maintenance and repair, so that decisive measures against electric shock must be taken.
In order to overcome this problem, for example, a circuit switchgear such as a fuse box serving as a safety plug, by which a conduction of a high-voltage circuit is electrically interrupted has been arranged in a conventional electric car. Therefore, the operator opens the cover of the fuse box before servicing the car such as making a circuit inspection and replacing fuses, so that safety can be ensured.
Such conventional fuse box serving also as the safety plug is shown in FIGS. 6 and 7.
As shown in FIGS. 6 and 7, a fuse box 101 includes a housing 102 in which a pair of terminals 112 arranged at a predetermined distance. The housing 102 has a rectangular shape and is formed from an insulating material. The terminals 112 have wires 115 connected to the rear ends thereof, respectively. As shown in FIG. 8, terminals 112 each has a holding portion 113 which is formed by press-working a metal sheet and is substantially U-shaped so that the holding portion 113 is resiliently deformable. Further, the terminals 112 each has an LA terminal 117 having a wire clamping portion 116. A wire 115 is connected to the wire clamping portion 116 formed at one end portion of the LA terminal 117, and the holding portion 113 is connected to the other end of the LA terminal 117.
On the other hand, a cover 104 is pivotally arranged on the upper portion of the housing 102. A cylindrical fuse 107 shown in FIG. 9 is fixed to an inner surface of the cover 104 with a band 109. The fuse 107 has a pair of fuse terminals 107a formed on both end portions thereof, the fuse terminals 107a are arranged so as to be engageable with the holding portions 113 of the terminals 112, respectively, when the cover 104 is closed.
Therefore, when the cover 104 is opened, the fuse box 101 disengages the fuse terminals 107a from the terminals 112 that are respectively connected to the wires. As a result, the wires are put into electrically interrupt conduction. Accordingly, the circuit can be broken completely as well as safely.
In the above constructed conventional circuit switchgear, a contact reliability between the fuse terminals 107a and the terminals 112 connected to the wires depends greatly on a resilient efficiency of the holding portions 113 which is designed to hold the fuse terminals 107a therebetween, and a dimensional accuracy of the fuse terminals 107a. However, since a thickness C of the fuse terminal 107a (see FIG. 9) is not specified for a connecting terminal, a wide range of tolerances is usually given to such thickness. Accordingly, it is difficult to ensure the reliability of contact between the fuse terminals 107a and the holding portions 113.
Furthermore, at the time of replacing fuses, a fuse 107 attached newly to the cover 104 must be fixed with a band while correctly regulating the position thereof so that the fuse terminal 107a is inserted into the holding portion 113 vertically. Accordingly, there is a possibility to lose the resiliency of the holding portions 113 by unnecessarily expanding the holding portions 113. In addition, it may be caused that the holding portions 113 will not be engageable with the fuse terminals 107a. Hence, an enormous amount of time and attention has been entailed for the fuse replacing operation.